If you feel like buying more (hehehe), you can also look for a product called Feliway. It's a diffuser or a spray that contains a liquid which contains pheromone from a mother cat nursing the small kittens. The diffuser is best cause it lasts one month for a room.
You can use it to calm the cat down and eliminate the stress as well.
It can be found at any PetSmart stores.
Like these two: